I mad my sump out of a 20 long. Since space is limited. First I picked a skimmer. I went with a eshopps s-120. So I made my first chamber 8" wide to fit the skimmer a heater and a filter sock. The second is a refugium that is about 12" long and the rest is return. I mad my baffles1" apart and with one up a 1" on either side for a bubble trap